The ARF Tumor Suppressor

描述(申请人提供)：ARF肿瘤抑制蛋白由INK4A/ARF基因编码，该基因是人类癌症中第二频繁突变的遗传位点。到目前为止，对ARF的研究主要集中在其肿瘤抑制功能上。相反，这项建议将重点放在我们最近发现的ARF的一个新的生存函数上，该函数存在于P53突变/缺失的肿瘤子集。我们证明ARF在饥饿诱导的自噬中起着不可或缺的作用。自噬是一种自我分解的过程，它促进了暴露在营养剥夺下的细胞的存活。由于肿瘤细胞存在于独特的新陈代谢压力条件下，许多肿瘤细胞严重依赖这一途径才能生存。与这一事实相一致的是，自噬抑制剂已显示出作为抗癌药物的前景。我们发现ARF蛋白在营养剥夺的反应中显著上调。我们发现，沉默ARF阻碍了自噬，并降低了营养缺乏细胞的存活率。最后，我们发现，在淋巴瘤中沉默ARF会损害自噬和生存，实际上会阻碍这些肿瘤的发展。这一提议的中心假设是ARF介导的自噬被带有突变型p53的肿瘤亚群利用，以使它们能够在代谢应激状态下存活下来。我们认为，对自噬生存功能的要求是肿瘤的一个致命弱点。我们需要更好地了解这一途径，以便将其用于癌症治疗。在拟议的研究中，我们将阐明ARF诱导自噬的机制(S)。我们将确定营养缺乏如何导致ARF蛋白水平增加。我们发现ARF的表达对某些肿瘤(淋巴瘤)是有益的，但对其他肿瘤(肉瘤)却没有好处；我们将定义从ARF介导的自噬中受益的肿瘤的子集。我们将确定自噬的关键介质，如ARF和Beclin1，是否决定了肿瘤对调节这一过程的小分子的反应，如氯喹(抑制自噬)和海藻糖(诱导自噬)。最后，我们将阐明P53对ARF基因转录抑制的机制，因为这导致了P53突变肿瘤中ARF的上调。合并后的数据将成为探索自噬途径用于癌症治疗的必要基础。

DESCRIPTION (provided by applicant): The ARF tumor suppressor protein is encoded by the Ink4a/ARF gene, which is the second most frequently mutated genetic locus in human cancer. To date the majority of research on ARF has focused on its tumor suppressor functions. This proposal focuses instead on a novel survival function for ARF that we have recently uncovered, and that exists for a subset of tumors with mutant/null p53. We show that ARF plays an integral role in starvation-induced autophagy. Autophagy is a self-catabolic process that promotes the survival of cells exposed to nutrient deprivation. Because tumor cells exist under uniquely metabolically-stressed conditions, many rely heavily on this pathway in order to subsist. Consistent with this fact, autophagy inhibitors have shown promise as anti-cancer agents. We show that ARF protein is markedly up-regulated in response to nutrient deprivation. We show that silencing ARF impedes autophagy and decreases the survival of nutrient-deprived cells. Finally, we show that silencing ARF in lymphomas impairs autophagy and survival, and actually impedes the development of these tumors. The central hypothesis of this proposal is that ARF-mediated autophagy is utilized by a subset of tumors with mutant p53 to allow them to survive episodes of metabolic stress. We contend that the requirement for the survival function of autophagy is an 'Achilles heel' for tumors. We need to better understand this pathway in order to exploit it for cancer therapy. In proposed research we will elucidate the mechanism(s) whereby ARF induces autophagy. We will determine how nutrient deprivation leads to increased ARF protein levels. We have found that ARF expression is beneficial for some tumors (lymphoma) but not others (sarcoma); we will define the subset of tumors that are benefited by ARF-mediated autophagy. We will determine whether critical mediators of autophagy, such as ARF and Beclin1, dictate tumor response to small molecules that modulate this process, such as chloroquine (inhibits autophagy), and trehalose (induces autophagy). Finally we will elucidate the mechanism of transcriptional repression of the ARF locus by p53, as this leads to ARF up-regulation in p53-mutant tumors. The combined data will serve as a necessary foundation for exploiting the pathway of autophagy for cancer therapy.